I will offer up what worked for me. I was getting the problem anywhere from 1 minute to 30 minutes after starting explorer. It especially occurred after hitting a 'complex' site.

After several months of this, and with no luck in finding a solution, I reviewed what had changed. The only thing had been the loading of anti spam software from Symantec. I unloaded the software and, voila, the problem disappeared. (plus speed was much better)

I suggest anyone else with the same type of problem look at what 'monitoring' type software has recently be loaded and start from there.

Hope this helps.